In the construction industry for commercial and residential buildings it is often desirable, especially for decorative purposes, to provide artfully curved and configured structural pieces or moldings. Particularly in the aircraft industry and to some extent in the automobile industry, it is desirable to provide smoothly curved structural members that enhance the development of controlled aerodynamic construction of aircraft and automobiles. Particularly in the construction industry for commercial buildings and enhanced grades of residences, it is desirable to provide windows having curved upper portions, sometimes of arcuate configuration, and in many cases of a substantially elliptical configuration, where, for decorative and structural purposes, the windows and doors may have a form of multiple varying curvature, perhaps incorporating sections of curvature of differing radii or being of varying curvature throughout the entire length thereof.
Historically, curved windows and doors have been manufactured for an extensive period of time, typically having the window frame portions thereof composed of wood that has been formed by any number of differing processes. More recently, aluminum door and window frame molding has been developed to thus provide for reasonably low-cost windows and doors having relatively low maintenance requirements. Where, for decorative purposes, such aluminum windows and doors are desired to have an artfully curved configuration, for example, of arcuate or substantially elliptical configuration, it is desirable to achieve controlled bending of straight aluminum strip stock which has been previously painted or otherwise coated to achieve a desired color and appearance. Aluminum strip stock for straight and curved window configurations is commercially available in any of a number of cross-sectional configurations, some of which are of very exotic design. To place or secure window and door frames, they are typically secured in position by means of screws, nails, staples, etc. Accordingly, the extrusions are provided with nail fins which are typically fairly thin and are easily penetrated by nails, screws and staples. In some cases certain nail flanges or nail fins are capable of being readily broken away so as to render the window or door frame convertible to different types of installations. Where curved or elliptical door or window frames are desired, it must be possible to achieve controlled bending of the strip stock without in any way distorting or tearing break-away nail fins.
Strip stock for any one of a number of different purposes is formed by bending it to a desired configuration by means of three basically acceptable processes, i.e., stretch-forming, forming by means of roll benders and bending through the use of eutectic alloys.
Although stretch forming is widely utilized for the bending of metal aircraft components, the cost of metal forming machines and their toolings, and the time required for special sizes, typically rule out this method for the window industry. Further, stretch-forming typically causes the material being formed to be necked-down, i.e., non-uniformly reduced in dimension, thus causing the resulting curved or formed product to have loss of dimensional quality. In the window industry where the extruded and painted strips being formed are of small or thin cross-sectional configuration and typically require interfitting of parts, a resulting condition of necking-down of material can not be tolerated. Loss of dimensional quality of the strip material will typically be clearly evident in the resulting product purchased by the ultimate consumer. Basically, stretch-forming occurs by placing the member being bent in tension and applying sufficient tensional force to remove any wrinkles or unusual distortion that is formed in the strip material during the bending process. Further, the stretch-forming process typically induces significant hardening of the strip stock material during bending. In the aircraft industry, bent parts may be annealed, i e., softened, after having been formed. Thus, the resulting annealed, bent or formed product has no particularly enhanced tendency for stress or wear damage during service. In the window industry, the strip stock is typically painted or coated prior to bending. Thus, the resulting bent or formed strip material can not be annealed after it has been formed. In essence, stretch-forming is a process for achieving bending of strip stock that can not be employed by the window industry for the development of curved or elliptical window frame components.
The process that is currently utilized for the forming of curved or elliptical window frame components is the roll forming process. The coated strip stock is passed through a roll forming assembly where it is formed to a curved configuration by passing it through a forming roll assembly. Although roll benders such as C.N.C. Roll Benders can be successfully operated for the forming of curved door and window components, the costs of these types of machines is typically extremely high. Further, it is necessary to have experienced operators with extensive operator skills in order to achieve satisfactory results. Consequently, labor costs for controlled bending of door and window components is extremely high. It is also well known that repeatability of the bending process is quite poor. It is difficult to achieve roll forming of successive aluminum strip stock and yet have the resulting curved product be precisely the same as another that is bent using the same strip stock and the same bending roll setting. For efficient commercial window and door manufacturing operations, it is necessary that the bending process achieve bending results that are duplicated. As mentioned above, the strip stock being bent is typically painted while in its straight form. For the resulting product to be of quality nature it is necessary that the paint on the strip stock not be damaged by scuffing, flaking, etc. It has been determined that significant damage to the finish of the material is often the result of many metal strip roll forming processes. This is an intolerable condition in the window industry because the resulting product must be aesthetically pleasing to the purchasing customer.
It should be born in mind that aluminum strip stock for the window industry has variable hardness, with hardness variations between batches of strips and with differing hardness from strip to strip within batches of strips. Hardness variation accentuates the strip bending problems that are encountered. With roll forming machines it has been determined that the strip material being bent is not only formed by contact with the rolls but it is also formed between the various rolls by the forces that occur. When the material is formed between the rolls it is not supported in any manner whatever. The resulting finished product can therefor be twisted or its curvature may vary from the curvature that is desired. The variations in material hardness that are encountered accentuate and amplify the roll bending problems that are encountered primarily because the bending being accomplished at any given time is confined to a very short length of the strip material. The roll forming process also causes extensive work hardening of the material being bent. For example, strip stock with a hardness of T-3 can easily be hardened to a hardness level of T-16 during the roll forming process. Because the strip stock has been significantly work hardened to this extent, if the resulting product varies slightly from the intended curvature for which the bending machine is set, the material will have work hardened to the extent that it can not be further formed. In this case, the material simply becomes scrap. High scrap rates are typical when aluminum strip stock for windows is being roll formed for arcuate or elliptical window frames.
It is also well known that expensive three roll die sets are necessary to accomplish forward, reverse and bow bends in aluminum strip stock. Although the roll bending machines are of quite expensive nature and the dies are significantly expensive, no manufacturer of these types of machines will provide a guarantee of success in the use of a machine or dies. Thus, many purchasers of the machines and dies can, and frequently do, produce a substantial quantity of scrap metal while attempting to set the machine up for a particular strip stock bending process. It is desirable therefore to provide a process and apparatus for accomplishing controlled bending of metal strip stock which is capable of producing designed, curved or elliptical components for windows, doors and the like without damaging the paint or coating of the strip stock and without wasting a considerable amount of the strip stock in order to achieve bending thereof. It is also desirable to provide a bending process and apparatus that achieves efficient, controlled and repeatable bending of strip stock such that any number of completed curved window or door components may be prepared in a short period of time.
Eutectic alloys are utilized in the bending of metal strips by initially suspending the strip within an elongate trough. Eutectic alloy in its molten or liquid state is poured into the trough so as to completely encompass the strip material to be bent and is then caused to solidify. Because the eutectic alloy becomes brittle when it solidifies, it must be quenched to permit its bending. The quenching step actually anneals the eutectic alloy to prepare it for bending. After its annealing and removal from the elongate trough, the annealed eutectic alloy with the strip material encapsulated therein is bent about a suitable form or is bent by passing it through bending rolls. After the bending process has been completed, the eutectic alloy is then again reduced to its molten state and is separated from the bent metal strip. One of the principal disadvantages of this bending process is that a small amount of the very expensive eutectic alloy remains on or in the strip stock. The loss of this expensive alloy has a significant disadvantageous impact on the cost of the bending process. Further, in some cases, it is necessary to insure removal of all of the eutectic alloy. In these cases cleaning of the bent strip stock can be quite expensive. Also, secondary bending of the eutectic alloy is not normally possible because it work hardens and again becomes brittle as it is bent. A further disadvantage, the equipment that is necessary to melt, fill, recapture, quench and handle the eutectic alloy is quite expensive and is also considered to be quite hazardous to worker personnel. All of these features render the use of eutectic alloys for the bending of metal window stock to be disadvantageous to the extent that it is impractical for the metal window industry.
Although much of the discussion in this patent concerns the controlled bending of strip stock material for windows, doors, and the like for commercial and residential buildings, the principles of this invention are equally effective for bending aluminum and other strip materials for the aircraft industry, the automotive industry, etc. Moreover, the principles of the present invention are applicable to the bending or otherwise forming of materials other than metal. For example, wood bending (laminating) equipment and equipment for laminating and forming of polymer materials may be effectively utilized within the scope of the present invention.